Reliable Data Transfer Sender

The sender has two state variables:

windowStart (initial value 0) is the start index of the send window.
nextSequenceNumber (initial value 0) is the sequence number to be used for the next outgoing packet.

The sender has one state variable:

nextSequenceNumber (initial value 0) is the sequence number to be used for the next outgoing packet.

Give the packet sequence number nextSequenceNumber and send it. Save the packet in case it needs to be resent.

Start the timer.

Start timer nextSequenceNumber.

Increment nextSequenceNumber and stop accepting input from the application layer if the window is full.

Increment nextSequenceNumber and stop accepting input from the application layer.

Advance the window to begin at the first unacknowledged packet.

Accept data from the application layer if the window has advanced.

Advance the window to begin at the first unacknowledged packet.

Accept data from the application layer.

Ignore it. It is an acknowledgment of a resend due to a late acknowledgment.

Send the saved packet and restart the timer.

Send all unacknowledged saved packets and restart the timer.

Send the saved packet associated with the timer and restart the timer.

Send the first unacknowledged saved packet and restart the timer.

	Alternating Bit	Go Back `n`	Selective Repeat	Cumulative Acknowledgment
Sender initialization
Response to a packet from the application layer
Response to an acknowledgment with an expected sequence number
Response to an acknowledgment with an unexpected sequence number
Response to a timer firing